<!DOCTYPE html>
<html>
	<head>
		<meta charset="utf-8">
		<title></title>
		<style type="text/css">
			
			.div2{
				background-color: green;
				margin-top: 2px;
				margin-bottom: 2px;
			}
			div{
				width: 100px;
				height: 100px;
				background-color: blue;
			}
			/* id选择器 */
			#div2Id{
				background-color: yellow;
			}
		</style>
	</head>
	<body>
		<div></div>
		<!-- id唯一标识一个标签 -->
		<div class="div2" id="div2Id"></div>
		<div></div>
	</body>
</html>
